Light emitting diode (LED) lighting systems are becoming more prevalent as replacements for existing lighting systems. LEDs are an example of solid state lighting (SSL) and have advantages over traditional lighting solutions such as incandescent and fluorescent lighting because they use less energy, are more durable, operate longer, can be combined in red-blue-green arrays that can be controlled to deliver virtually any color light, and generally contain no lead or mercury. In many applications, one or more LED dies (or chips) are mounted within an LED package or on an LED module, which may make up part of a lighting unit, lamp, “light bulb” or more simply a “bulb,” which includes one or more power supplies to power the LEDs. An LED bulb may be made with a form factor that allows it to replace a standard threaded incandescent bulb, or any of various types of fluorescent lamps. LEDs can also be used in place of florescent lights as backlights for displays.
Many LED lamps use a reflector or a combination of reflectors to bounce light off a surface or surfaces before it is emitted from the lamp. This bouncing has the effect of disassociating the emitted light from its initial emission angle. Typical direct view lamps emit both uncontrolled and controlled light. Uncontrolled light is light that is directly emitted from the lamp without any reflective bounces to guide it. According to probability, a portion of the uncontrolled light is emitted in a direction that is useful for a given application. Controlled light can be directed in a certain direction with reflective surfaces. The mixture of uncontrolled and controlled light defines the output beam profile. In a “retroreflective” arrangement, light from the source either bounces off an outer reflector (single bounce) or it bounces first off an inner or secondary reflector and then off of the outer reflector (double bounce). Thus, most of the light is redirected before emission and controlled.
A reflector for a solid-state lamp can be constructed in various ways. Sheet metal such as aluminum can be used. A reflective film fastened to a substrate with adhesive can also be used to form a reflector. Vacuum metalized plastic (PVD) is commonly used in lighting because of its low cost and relatively good performance. Sputtered metal coating affords the opportunity to provide high reflectivity by using highly reflective metal such as silver as the sputtered metal. A base coat is applied to the plastic prior to sputtering. The thickness of the base coat can obscure fine details of the reflector, so that sputtered metal coated plastic may not be suitable for reflectors with complex surfaces.